Electric furnace



New. 10, 1931- H. ALTSHULER ETAL 1,831,054

ELECTRIC FURNACE Filed April 23. 1928 4 Sheets-Sheet l Nov. 10,1931. ALTSHULER ETAL 1,831,054

ELECTRIC FURNACE Filed April 23. 1928 4 Sheets-Sheet 2 1931- H. I. ALTSHULER ETAL 1,831,054

ELECTRIC FURNACE Filed April 23. 1928 4 Sheets-Sheet 3 Nov 10,1931.

H. I. ALTSHULER ETAL ELECTRIC FURNACE A 4 lllll "u u Patented Nov. 10,1931; I

Nlrsoj srarss rrlcs may 1 Americana a; :aamz, or menace, moo

' anaemic summon The present invention relates to. electric furnaces and methods of operating thesame.

. One of. the'objects of the present invention" is to provide an electric'iurnace which is ea I; able of'producing high ,temper'atur'esfover ong periods without nndue loss of heat or deterioration of the resistor material.

Another object of the present invention is to protect the resistor material, from change or destruction, at thesametime afiording convenient access to tlie same for the purposeof replenishment, ormanipulation.

Another object of the present invention is to provide an electric furnace and method of operating the same'whereby the temperature may be accuratel adjusted and'maintained at a predetermine unrformvalue even under widely varying demands.

With these and other objects in view, as

will hereinafter appear, one feature of the invention consists of an electric furnace of the resistor type in which the similar resistor material is contained within a completely sealed enclosure, the material to be heated being dis osed externally of the resistor enclosure. he complete enclosure of the resistor material not onl protects the armies against oxidation y access of air, ut also contributes to the uniformity of tem erature of the heated substances because of t e elimination of varying temperature efiects occurring by virtue of air circulation around the resistor.

'Another feature of the invention-consists in the provision of a plurality of heating chambers arranged externally of the resistor box and substantially protected against circulatory currents of air. The heating chambers are completely separated from each other in order that circulating currents may not enhance the heating of an one chamber at the expense of another. ubstantially the only heatto which the substances in theheating chambers is sub'eeted, therefore, re the heat radiated from t e adjacent portions of the resistor box.

A still further feature of the invention comprises a temperature control by which the temperature is maintained substantially constant over long periods and under varying de- ,l928. Eteriai H 87%,122.

mands, The method of control consists in maintaining the current through the resistor material su determined experimentally that maintenance of constant current in a furnace of this type serves effectively to keep the heatin temperature substantially uniform. The s stantially constant; It has been ature of temperature control by constant current is simpler than attempted control by automatic devices operated directly from the furnace temperature and'iurther ofl'ers the advantage that upon a variation in temperature following'a change ,in the demand on the furnace or a variation-in the resistor, it restores the temperature to its predetermined value in a nnmmum of time, and without causing fluctuations or oscillations of temperature above and below the normal value.

Y Although any usual means for maintainin constant current in a circuitmay be'em loyed for efiecting the above method, an additional featureof the invention comprises a preferred apparatus by which the current is automati- .cilly' held at the predetermined value neces- ,sary for maintenance of the desired temperature.

(Ether features of the invention consist certain novelfeatures of construction, combmations and arrangements of parts hereinafter described and particularly defined in the claims. I p

in the accompanying drawings illustrating What is now considered to be the'preferred ,form of the invention, Fig. 1 is a vertical,

longitudinal, sectional view of the furnace in two planes as indicated by line 1-1 of Fig. 2;

i the illustrated and described herein, the invention comprises a furnace for heating drill and sharpening. The heating element comprlses a mass of granular carbon resistormaterial to whichcurrent is conducted by carbon electrodes. The granular material is contained in a trough which extends longitudinally throughout the length of the furnace, the trough being completely covered and closed to prevent access of air. The heating chambers into which the ends of the drills are introduced are eight in number, four at each end of the furnace, symmetrically dis osed above and below and on each side the furnace. Each chamber is separated from the other chambers by suitable vertical and horizontalpartitions, and is formed tofacilitate the introduction and withdrawal of the work to be heated, at the same time avoiding unnecessary loss of heat.

Referrin to the drawings, the granular carbon resistor material 6 is enclosed in a box comprising two opposed troughs, a lower I trough 8 and upper trough- 10, both of a refractory insulating compound. The troughs are separated by close fittinghorlzontai partitions 12 which close the 'oints between the troughs and extend latera y in a horizontal direction to form partitions for the heating chambers, as shown in Fig. 3. The bottom trough is supported on a series of blocks 14 arranged longitudinally of the furnace and a series of similar blocks 16 rests upon the u per trough. The current is conducted to t e resistormaterial by carbon electrodes 18 supported in any usual or preferred form of bracket 20 arranged externally of the fur- I ing chambers are defined by wall forming the lower boundary of the heating chambers. This wall, as shown in Fig. 3, comprises two rows of refractory brick 26, such as magnesite, one row on each side of the furnace. These blocks serve as rests or supports for the drill steels which are to be heated. Between the rows of blocks 26 IS a central row of blocks 28 resting on a row of magnesite blocks'30 which are embedded in the cement. The blocks 28 serve as supports on which thelongitudinal partitions 14 rest. The spaces between the blocks 26 and 30 are filled with rows of refractory blocks 32.

The drill steels which are to be heated comrise a long shank 34 terminating in an en: lhrged point or head 36. The shanks 34 are adapted to rest on the blocks 26, and also upon ametal table 38 which is secured to the outer wall of the furnace and supported by a diagonal brace 40, also attached to the outer wall. The blocks 28 are beveled as indicated at 42 to provide surfaces against which the 46 as shown in Fig. 1. i The brick is so formed as to provide a port which at its center is of only sufiicient height to accommodate the diameter of the drill shanks as indicated at 47. To provide for admission and removal of the drills in the heating chamber, the port is enlarged'at its ends 48 by a reduction in the thickness of the cover block 44.

In operation of the furnace, the drills are introduced one at a time at short intervals through one of the enlarged and portions 48 of the port and, as the heating progresses, are moved bodily into the restricted space 47, as the heated drills are removed one by one from the other end. As shown in F i 3, the ports 47 are arranged in two tiers on both sides of the furnace and are conveniently positioned so that a. single operator may 0perate two or all four chambers on one side of the furnace. The restriction of the port, except at its ends, to a height only sufiicient for accommodation of the drill shanks prevents excessive access of air to the heating chamber. The fire brick 44 above the ports 47 serves also as a support for the furnace side wall 50 which comprises a number of layers of refractory insulating material arranged in rows longitudinally of the furnace. As shown in Fig. 3, the inner surface of the wall 50 abuts against the partition 12, and is set back from the side walls of the trou he 8 and 10 adjacent thepartition 12, to en ar e the heatin chambers on each side of t e troughs. n the top of the wall 50 is arranged a row of magnesite blocks 52 similar to the blocks 26 and serving as rests for holdmg drill steels in the upper heating chambers. In identical fashion with the constructlon of the lower heating chambers,- the ports 54 for admission of the drills are defined by a cover block 56 of the same shape as the block 44. Tables 57 identical with the tables 38 are provided to support the drill shanks.

The upper wall of the furnace indicated generally at 58 is made up of layers. of rows of brick of insulating refractory material supported by the partition'members 16 and the fire brick cover blocks 56. V

It will be seen that each end of the furnace is divided longitudinally into the four heating chambers, each indicated at 60 in Fig. 3, and separated from eachgother by the longitudinal partitions 12, 14, and 16. These four chambers at one end of the furnace are separate from a corresponding set of similar chambers at the other end of the furnace by means of a transverse partition as shown in Fig. 4, which comprises a set of blocks 62 formed to fill the spaces between the trough and the-furnace walls. The furnace there fore has eight heating chambers of identical form, each completely separated from the others. by the various partitions which prevent all circulation between them. At the center, the bottom Wallis bored to receive tubes 64 which act as protecting tubes for pyrometers.

The electrodes 18 are admitted to contact with the resistor material through electrode boxes 66, one at each end of the furnace. The electrode boxes, which are alike for both electrodes, are supported upon the foundation which is extended at its ends beyond the ends of the trough 8. As shown in Fig. 5, it comprises an enclosure of fire brickhaving a bottom wall 68, a top wall or inwardly extending ledge 70, and two side walls 72. These bottom and side walls abut the end of the lower trough 8 and the top wall abuts the ends or the horizontal partitions. '12. On top of the electrode box is a filling port comprisin a fire brick box having side walls 74; an a top wall 7 6, its bottom being formed by the top wall 70 of the electrode box. This port opens directly into the trough and is provided for the purpose of permitting access to the trough in order that renewal or stirring of the resistor material or repairs to the trough may be readily effected. During" normal operation, the port is closed by blocks of tire brick 78 which are sealed at the joints by cement 80.

The entire structure is enclosed in a steel shell indicated generally. at 82. The shell providesthe support for the work supporting tables 38 and 57, and also for the electrode supports 20. The shell is not continuous but comprises upper and lower portions 8d and 86' which as shown in Fig. 1, are separated b a layer of non-magnetic insulating materlal 88 to prevent the formation of large magnetic fluxes in the shell, which fluxes might give rise to high'electrical losses by the flow'of eddy currents. Tn order to prevent excessive radiation from the top of the furnace, the shell is spaced some distance from the top wall and this space is filled with heat insulating powder 90.

In operation, the furnace is energized by the flow of current between the electrodes 18 and through the granular resistor. .Jhe drills large number of drills are being i e to be heated are inserted into the arts ll through one of the enlar ed'end po tions as, and as they become heate to proper temperature are successively removed through other end of the port, the remain 1 being movedlaterally and a new r i g inserted every time a heated drill is removed.

As thus described, thefurnace is su" some fluctuation in temperature.

demands on the furnace will increase the temperature will tend to drop. 1 variation is likely to occur because of in the resistance of the resistor material.

The material has a negative temperature coeflicient which results in a decreased resistance as the furnace warms up and, moreover, the resistance is subject to variation upon occurrence of mechanical shock. Control of temperature by maintenance of constant current has been found to give a substantially uniform temperature even though the demands on the furnace may vary considerably. In its broader aspects, the invention contemplates the method of control by maintenance of constant current, however the uniformity of the current may be obtained, and it is therefore within the scope of the invention to employ well-known devices for this purpose, such for example, as a constant current transformer. However, because of its simplicity and accuracy of control, the system shown in Fig. 6 is preferred.

This preferred control apparatus comprises an automatically variable impedance, consisting of a reactor coil 9% which is in series with the furnace electrodes 18 and which has a movable core 96. The alternatmg current line 98 which serves to energize the furnace connects through a current transformer 100 with an ammeter 102. A second current transformer 10 1 is connected with automatic devices for moving the core 96 with respect to the reactor winding 94.

The terminals of the secondary of the current transformer 104 are connected with a relay which comprises a coil 106 and a movable core 108. The winding 106 is shunted by a rheostat 110. The current flowing through the relay 106 is determined by the rheostat 110, and the setting of the rheostat will determine the value of current at which the relay 106 will operate, and consequently the temperature which the furnace will con stantly maintain.

The core 108 of the relay is connected with a movable switch member 112 which is adapted for engagement with-one of two opposed contacts 114-. /Vhen the current is of the proper value, the switch arm 112 lies between the contacts 114; without making contact with either but ii the current should increase, the core 108 will be attracted the relay coil 1063, thereby closing the switch on the upper contact 114,-. Similarly, a decrease in current will close the switch on the lower contact. through the switch arm 112 and z switch relay on the up I the SWlllCll 1 a reversing being mamas ,to two sets of fixedcontacts 128' and 130, the

latter being connected to the three phases'of the motor. The movable contacts 123 are connected with the three-phaseline 124 and-- the contacts 128 are connected with the contacts 130, as shown in Fig. 6, in such a manner that closure of the reversing switch on the contacts 130 reverses two of the phases, thereby reversing the direction of rotation of the-motor.

Normally when the current invthe line 98 is of the proper value, the reversing switch is open and the motor is stopped. The motor shaft connects through a pair of bevel gears 132 with a shaft 134;. which is threaded through a nut 136 on a vertically movable member 138. The member 138 is connected by d cord 140 passing over pulleys M52 with the reactor core 96. Upon a change of rent from its predetermined value, reactor core is therefore automatically moved or out of the reactorwindin i Thus when the current increases, the core is permitted to move farther into the winding to increase the reactance ahd thereby to limit the current until the switch 112 again opens and stops the motor. Similarly, upon a decrease of current, the core 96 is'retracted and the reactance is decreased until the current is brought to its original value.

Although it is generally assumed that constant temperature may be maintained by a constant power input, the advantages of constant current control may be made apparent by considering an example of a condition where the demands upon the furnace are sub ject to a considerable variation. Suppose the furnace to have been operating at a constant temperhture to heat a moderate number of drills. If now it becomes necessary to increase the demands on the furnace by introducing an increased number of cold drills, a larger amount of heat will be required and the abstraction of this heat will cool the resistor. The carbon resistor has a negative temperature coeiiicient and upon cooling, its resistance increases. thereby tending to decrease the current through it. This decrease in current sets automatic control devices ration the current is thereby reto original value. The power suprnacc is thus increased under resistance or" the resistor. pewer results in an increased restored to sistance the r decreases and Wlill it the power, the current ined substantially constant at seems;

its original value at all times. If it were attempted to adjust for constant power at all times, itwill be seen that when the resistance of the granular material increases following an increase of load on the furnace, the current will be somewhat decreased and the power input will be lower than in the case of constant current control, thereby requiring a longer time to bring the heating clfambers to the proper temperature.

Similarly, if the load on the furnace is suddenly decreased by removal of a large number of drills, the furnace tends to heat up and the resistance decreases; The supply of constant current to the resistor, according to the present invention, results in a decreased power input which permits the furnace tem perature to be restored quickly to its normal value under the decreased load; whereas if a constant amount of heat were dissipated in the resistor by maintenance of constant input, the furnace would require a considerable time to cool to the proper temperature for the dr will be seen that the furnace of the present invention is not only simple, but is one great durability because the charge of resistcr material is not subjected to oxidation by access of air. Moreover, because of the isolation of the material to be heated from the resistor, there is no possibility of chemical change due to interaction of the resistor by contact with the heated material or gases or vapors given off therefrom. The separation of the heating chambers prevents circulation of air between them, which circulation might tend to heat the various chambers to unequal temperatures. The heating chambers are, therefore, brought to a tem-' perature determined principally by the radiant heat emitted from the resistor. This radiant heat is substantially uniform in all the heating chambers and is capable of accurate control,

The invention has been illustrated and described as embodied in a specific form of furnace utilized for heating drill steels, as its construction and control adapted it particularly for such or some analogous use when the work requires uniform heating within close temperature limits. It is understood, however, that the invention is not limited to this particular use or to the specific arrangement of parts except as limited by the claims but be employed for other and diiierent kinds of work and may be constructed in differen forms.

'lhc invention having been thus described, what is claimed is:

An electric furnace comprising a completely enclosed container, granular resistor material in the container, electrodes for con ducting current to the resistor material, furnace walls surrounding the container and constructed to form heating space adjacent the container, and partitions in said space to form a plurality 0 separate heating chambers.

2. An electric furnace comprising a foundation, side walls and a top wall, a resistor trough enclosed by the furnace walls and spaced therefrom, means for supporting the trough acting as partitions to divide the space between the trough and the walls into a plurality of separate, non-communicating, heating chambers, and means for supporting articles to be heated in the heating chambers.

3. An electric furnace comprising an en closed container for granular resistor material, electrodes for conducting current to the resistor material, furnace walls surrounding and spaced from the container, vertical partitions and horizontal partitions extending between the container and the walls to divide the space between the container and the walls into separate heating chambers, and means for supporting articles to be heated in the heating chambers.

4. An electric furnace for heating drills comprising a trough, a body of resistor material received in the trough, furnace walls surrounding and spaced from the trough to form a heating space between the trou h and the walls, the wallshaving a port or admission of the drills, and means for ositioning the drill points externally o the trough and adjacent thereto.

5. An electric furnace comprising an enclosed container for resistor material, means at theends of the container having an electrode port and a filling port, devices for sup porting an electrode in the electrode port for contact with the resistor material, and a closure for the filling port.

6. An electric furnace comprising a container for a resistor, a wall surrounding and spaced from the container to form heating chambers externally of the container, the wall having an electrode port and a filling port at each end of the container, means for supporting the electrodes for contact with the resistor, and means for sealing the filling port.

7. An electric furnace for heating drili steels comprising a trough containing and completely closing a resistor, a wall constructed to form a heating chamber adjacent the trough and having a'drill admission port, the port having an en arged portion to admit the drill point and a restricted portion to accommodate only the drill shank with the drill point positioned in the space between the trough and the wall.

8. An electric furnace for heating drill steels comprising a trough containing and completely closing a resistor, a foundation on which the trough is supported, and a wall spaced from the trough to form a heatin chamber, the wall including a supporting block for the drills, and a cover block forming a drill admission port with a restricted central portion and an enlargement at each end, whereby the drills may be admitted through an enlarged portion and thereafter moved into the restricted part thereof.

9. An electric furnace comprising a container for completely enclosing resistor ma terial, the furnace walls havin admission openings, and partitions extending between the container and the walls to divide the space between them into a plurality of separate non-communicating heating chambers and thereby to prevent circulation of air between the admission openings.

10. An electric furnace comprising a container having an electrode port, an electrode, an inwardly extended ledge above the electrode, and a body of resistor material filling the'container above the level of the ledge, the container being completely enclosed above the ledge to prevent circulation of air above the resistor material.

In testimony whereof we have signed our names to this specification.

HENRY I. ALTSHULER. GROVER B. LANTZ.

- CERTIFICATE OF CORRECTION.-

Patent No. 1,831,054. Granted November 10, 1931, to

HENRY I. ALTSHULER ET AL. Q

It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows: Page 5, line 51, claim 7, for "closing'l read enclosing; same page, line 61, claim 8, for "closing" read enclosing; and that the said Letters Patent should be read with these corrections therein that the same may conform to the record of the case in the Patent Office.

Signed and sealed this 22nd day of December, A. 'D. 1931.

M. J. Moore. (Seal) Acting Commissioner of Patents. 

